Chronic Inflammation in Early Adulthood Correlates with Worse Cognitive Function in Middle Age

Short-term inflammation is a necessary part of the immune response to pathogens, injury, and problematic cells. Lasting unresolved inflammation is harmful, however. It is a feature of aging, but can also occur to significant degrees in earlier life as a result of autoimmunity or being very overweight. Researchers here show that early adult chronic inflammation correlates with worse cognitive function nearly two decades later. One can debate the degree to which this is a measure of accelerated degenerative aging versus the progression of existing conditions, but it is certainly true that chronic inflammation is to be avoided and minimized to the degree that it is possible to do so.

There are two kinds of inflammation. Acute inflammation happens when the body's immune response jumps into action to fight off infection or an injury. It is localized, short-term and part of a healthy immune system. Chronic inflammation is not considered healthy. It is a low-grade inflammation that lingers for months or even years throughout the body. It can be caused by autoimmune disorders like rheumatoid arthritis or multiple sclerosis, physical stress or other causes. Symptoms of chronic inflammation include joint pain or stiffness, digestive problems, and fatigue.

The study involved 2,364 people age 24 to 58. They were followed for 18 years. Participants' inflammation levels were measured at the start of the study and three more times throughout the study. The study looked at levels of C-reactive protein (CRP) in the blood. CRP is produced by the liver and increases when there is inflammation in the body. Researchers divided participants into three groups based on inflammation levels: consistently higher, moderate or increasing and lower stable. Of the total participants, 911 people, or 39%, had consistently higher inflammation; 381 people, or 16%, had moderate or increasing inflammation; and 1,072, or 45%, had lower stable inflammation.

Five years after their last inflammation measurement, participants were given six tests to examine thinking and memory skills. On a test that measures processing speed and memory, participants were given a key showing numbers and corresponding symbols. They then drew those symbols on a separate list of random numbers as quickly as possible. Of those in the low group, 10% had poor cognitive performance, compared to 21% in the middle group and 19% in the high group. After adjusting for factors such as age, physical activity and total cholesterol, researchers found that both the high and moderate groups were more likely to have poor performance in processing speed and executive function. For processing speed, researchers found that those in the moderate group were more than two times more likely to have poor performance and those in the highest group were nearly two times more likely to have poor performance than those in the lowest group. For executive function, those with the highest CRP levels had a 36% higher risk of poor performance.